[PATCH] generic/800: TEST_DIR, not TEST_MNT

["Darrick J. Wong" <djwong@kernel.org>]

From: Darrick J. Wong <djwong@kernel.org>

Fix this new test regression:

 --- /run/fstests/bin/tests/generic/800.out	2026-08-18 09:30:13.655513087 -0700
 +++ /run/fstests/logs/generic/800.out.bad	2026-08-18 16:30:24.107110215 -0700
 @@ -1,2 +1,4 @@
  QA output created by 800
 +/dio-read-source: Read-only file system
 +dio read failed
  Silence is golden

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
---
 tests/generic/800 |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tests/generic/800 b/tests/generic/800
index 52a664a17e448b..b79c1a0c052876 100755
--- a/tests/generic/800
+++ b/tests/generic/800
@@ -32,8 +32,8 @@ _cleanup()
 _scratch_mkfs >> $seqres.full
 _scratch_mount
 
-# Create the 4MiB target file on TEST_MNT as the read source.
-$XFS_IO_PROG -f -c "pwrite -i /dev/urandom 0 4M" "$TEST_MNT/dio-read-source" >> $seqres.full
+# Create the 4MiB target file on TEST_DIR as the read source.
+$XFS_IO_PROG -f -c "pwrite -i /dev/urandom 0 4M" "$TEST_DIR/dio-read-source" >> $seqres.full
 
 # Another 4MiB target file on SCRATCH_MNT as the mmap dest
 $XFS_IO_PROG -f -c "pwrite 0 4M" "$SCRATCH_MNT/mmap-dest" >> $seqres.full
@@ -42,7 +42,7 @@ read_workload()
 {
 	_register_cleanup "wait"
 	while true; do
-		$here/src/dio-read-into-mmap "$TEST_MNT/dio-read-source" \
+		$here/src/dio-read-into-mmap "$TEST_DIR/dio-read-source" \
 			"$SCRATCH_MNT/mmap-dest" &> /dev/null
 		if [ $? -ne 0 ]; then
 			echo "dio read failed"